Authors :
Presenting Author: Laura Rossini, – Epilepsy Unit, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milano, Italy
Cinzia Cagnoli, PhD – Epilepsy Unit, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milano, Italy
Dalia De Santis, PhD – Epilepsy Unit, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milano, Italy
Rita Garbelli, – IRCCS Foundation Neurological Institute Carlo Besta
Marco De Curtis, MD – Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy
Rationale:
Normal brain function is critically dependent on efficient mechanisms of clearance of excess K+ from the extracellular space released during neuronal activity; accumulation of extracellular K+ makes neurons hyperexcitable and may rapidly translate into epileptic seizures (Kofuji P, Newman EA. Neuroscience 2004; 129(4):1045-56). Spatial buffering depends on proper distribution and function of astrocytic potassium channels and gap junctions, normally localized on astrocytes, oligodendrocytes and in the myelin sheaths. We investigated the expression of connexins and potassium channels in type IIb focal cortical dysplasia (FCDIIb), a developmental malformation frequent cause of drug-resistant focal epilepsy and affected by a reduction of myelin.
Methods:
We studied post-surgical FCDIIb neocortical specimens (n=14) comparing lesion and perilesional area in the same tissue section using immunohistochemistry to evaluate the density and localization of the main glial connexins (Cx43, Cx32) and potassium channel (Kir4.1). Cryptogenetic tissue was also included as additional control (n=3). Moreover, with confocal super-resolution microscopy we investigated potassium channels localization in relationship with vessels and axons.
Results:
FCDIIb are characterized by profound changes in the expression and distribution of both connexins and potassium channels. The main alterations are: 1) Cx43 increased and the increase strictly correlated with the presence of gliosis; 2) Cx32 exhibited an aberrant expression in astrocytes and balloons, while its expression seemed to be lost in oligodendrocytes; 3) the potassium channel Kir4.1 maintained its cytoplasmic expression in glial cells, however it was dramatically reduced around vessels, in correspondence with the glial end-fits. Furthermore, its expression in the neuropil, and in particular around the axons, was irregular and discontinuous.
Conclusions:
Our results demonstrated in the core of lesion important abnormalities in gap junction/potassium channels suggesting an improper spatial buffering.
We can speculate that an ineffective potassium buffering and a consequent accumulation of extracellular K+ may amplify and sustained tissue hyperexcitability. Electrophysiological data will be necessary to validate this hypothesis.
Funding:
Supported by: European Union-Next Generation EU-NRRP M6C2-Investment 2.1 Enhancement and strengthening of biomedical research in the NHS, PNRR-MCNT2-2023-12377819 grant.